80. Thyroidectomy

Question 1

What are the anaesthetic problems of a patient who is thyrotoxic with a
large goitre presenting for thyroidectomy?

Answer 1

These may be divided into the effects of thyrotoxicosis and those of the goitre
on the airway and surrounding structures.

Question 2

Thyrotoxicosis

Answer 2

Cardiovascular
Tachycardia

Arrhythmias (esp. AF)

Congestive cardiac failure

Ischaemic heart disease

May be chronically hypovolaemic and vasodilated causing hypotension on induction

Exaggerated response to laryngoscopy and surgical stimulation with tachycardia, hypertension and ventricular arrhythmias

Question 3

Thyrotoxicosis

Answer 3

Thyroid storm See below

Eyes
Lid retraction, exophthalmos, conjunctivitis

Other
Proximal myopathy

Anaemia

Thrombocytopaenia

Hypercalcaemia

Abnormal glucose tolerance

Associated auto-immune disease, e.g. diabetes, myasthenia

Question 4

Effects of goitre

Answer 4

Compression

Airway
May be worse in supine position, eased on side or prone
Tracheomalacia (especially post-operatively

SVC
Retrosternal extension
Oedematous face and airway
Engorgement of nasopharyngeal veins (epistaxis with fibre-optic intubation)

Poor venous return therefore place i.v. line in lower extremity (IVC territory

Recurrent laryngeal nerve

1% have involvement pre-operatively. This causes cord
adduction leading to a hoarse voice.

Bilateral nerve involvement causes stridor.

Tumour invasion of local tissues

Question 5

How would you assess her thyroid status?

Answer 5

Weight loss, diarrhoea, vomiting
Restlessness, tremor
Palpitations
Heat intolerance
Eye complications (Graves’ disease)

Signs
Tachycardia
Atrial fibrillation
Cardiac failure
Warm, vasodilated peripheries
Goitre with bruit
Hyperkinesis

Investigations TSH ↓
T3 ↑
T4 ↑
Free T4 ↑
Thyroid scan (131I) – ‘hot’ or ‘cold’ spots

Question 6

Which drugs are used to manage thyrotoxicosis?

Answer 6

Carbimazole

Inhibits hormone synthesis.
Takes 4–8 weeks to work.
Major side effect is depression of the white cell count.
Agranulocytosis in 1/1000 after 3 months.

Propylthiouracil Inhibits hormone synthesis.
Also inhibits peripheral conversion of T4 to more active T3.

Given if sensitive to carbimazole.
Takes 4–8 weeks to work.
Side effects include leucopaenia, aplastic anaemia,
lupus-like syndrome.

Iodine (Lugol’s solution) Traditionally given for 10 days prior
to surgery to reduce the vascularity of the gland. This
practice is now less common because the thyroid gland
is dissected without transection.

β-blocker Propranolol controls cardiovascular effects and
decreases peripheral conversion of T4 to more active T3
Heart rate of less than 85 has been recommended
Atenolol or nadolol (both longer acting) may achieve
better control of symptoms

Question 7

How would you assess the airway?

Answer 7

Symptoms
Positional dyspnoea (esp supine with retrosternal goitre).
Dysphagia

Signs
Stridor
Routine assessment of expected difficulty with intubation.

Investigations
Indirect laryngoscopy or fibre-optic nasendoscopy by ENT
surgeon will give clues as to whether the larynx is likely to
be easily visualized at direct laryngoscopy.

Chest X-ray/lateral thoracic inlet – tracheal compression/deviation.

CT scan – extension of retrosternal goitre and site/degree
of tracheal compression. Diameter of airway at narrowest
point can also be measured.

Question 8

This patient was euthyroid with no clinical or radiological evidence of
obstruction. How would you anaesthetise them?

Answer 8

Pre-medication Benzodiazepine

-blocker continued

Standard i.v. induction and muscle relaxation is acceptable.

Care to obtund pressor responses.

Armoured tube – well secured

Attention to eye protection

Sandbag between shoulder blades

Head-up (reduces bleeding) and extended

Arms by the side therefore long drip extensions

Check cords at the end when breathing spontaneously – bilateral recurrent
laryngeal nerve damage will cause bilateral cord adduction and stridor.

Extubate ‘awake’.

Post-operative care to include attention to oxygenation, fluid balance,
analgesia, airway monitoring for signs of obstruction – clip remover
immediately available.

Check serum calcium and have i.v. calcium by the bedside.

Continue -blocker.

Question 9

What is thyroid storm

Answer 9

This is a life-threatening syndrome seen in hyperthyroid patients typically
6–24 hours post-operatively,
although it may occur intra-operatively.

It is characterized by
hyperpyrexia, tachycardia, hypotension and altered consciousness.

It may initially mimic malignant hyperthermia, but is not
associated with muscle rigidity or a rise in CK.

Other factors such as labour or severe infection may also precipitate the syndrome.

Question 10

thyroid storm treatment consists of:

Answer 10

Antithyroid drugs

Propylthiouracil – orally or N/G

Iodide – inhibits release of hormone from gland

Dexamethasone – inhibits synthesis, release and peripheral conversion

β-blocker Propranolol –
combined β1and β2 preferable
β1 Cardiovascular effects
β2 Suppresses metabolic effects
Reduces muscle blood flow and therefore heat production

Active cooling

i.v. fluids

Paracetamol

Invasive monitoring and inotropic/vasopressor therapy as indicated